(12C) Decimal to Fraction

[Thomas Klemm]

(08-08-2018 10:26 PM)Albert Chan Wrote:  dec2frac(2.0, 10) crashes with ZeroDivisionError. "if c < 2 and" should be "if c < 2 or"
-> since it is translated from calculator code, you might want to check this.

Nah, Joe is of course correct:

Code:

\<< DUP2 @ Must be two arguments.  Exit now if max denominator < 2,
  IF 1 > SWAP FP AND @ or if decimal fraction is an integer.

It's only me that should study De Morgan's laws.

Quote:Although not a bug in Python, when code running in a calculator, v can be huge.
-> v might be much bigger than c, corrected v below c might be off.

Below is the patched code:

Code:

def dec2frac(f, c):
    if c < 2 or int(f) == f: return
    u, v, F = 0, 1, f
    while f:
        f = 1/f
        w = u + v * int(f)  # check before update
        if w > c: break     # guaranteed v <= c
        u, v, f = v, w, f - int(f)
    q = u + (c - u)//v * v  # biggest quotient
    if diff(F, q) >= diff(F, v): q = v
    return int(q * F + 0.5), q

Not sure if I understand that correctly but that's something Joe might want to change in his RPL program as well. So this is rather a "jump forwards"?

Thanks for the feedback
Thomas